Researchers say this is the first time a cosmic event has been seen both with gravitational waves and with the full electromagnetic spectrum

Astronomers scanning ripples in space-time have detected the collision of two neutron stars for the first time—and, by analyzing the flare from the cataclysmic crush, discovered such stellar smashups are the source of gold, platinum, uranium and other heavy elements found throughout the universe.

The discovery, documented in a series of new research papers, was announced Monday at a news conference in Washington, D.C. The findings were the work of thousands of researchers at three sprawling gravitational wave detectors in...